Hypothetically, if an atheist opposed the gay lifestyle for philosophical but not religious reasons, and refused to make an Adam & Steve wedding cake, would the law allow him to defend his choice of associations?
Well, first, you moved the goalposts here, in a seemingly minor but significant way. You originally said:
It only protects business owners who don't want to serve social entities because of religious reasons. It does not protect everyone's right to choose associations for any reason.
There is a difference between the decision to sell or not to sell a cake to someone, and the decision not to create a cake for someone. In that difference you will find the primary grounds for a religious reason for doing one but not the other. I have maintained several times that if a homosexual person walks into a bakery, and asks to purchase a cake in the display case, and the baker refuses, then that is discrimination, and potentially actionable. (Bonus: to the extent that it IS actionable, this new law does absolutely nothing to change that.)
Nevertheless, I'm sure there is legal precedent that considers the relevance of first-amendment protections for religious beliefs to non-religious ideological beliefs. Were I making the rules, I would extend first-amendment protection the same to both religious and non-religious ideological beliefs.
I don't think this law moves the ball in either direction in this regard, though.